Process of classifying materials



Jan. 31, 1933. c. E. wUENscH PROCESS OF CLASSIFYING MATERIALS Filed Aug. l5, 1932 Patepted 311,

` UNITED STATES PATENT OFFICE' CHARLES ERB WUENSCH, F J'OPLIN, NISSOUBI, .ASSIGNOR lO MINEBALS BENEFIICIA- TION INCORPORATED, OF'J'OPLIN, MISSOURI, A. CORPORATION 0F DELAWARE I raocass or cmssmmc Marani-Ls Application med August 15, 1932. Serin No. 628,778.

. My invention relates Vto improvements in wet processes for gravitall separating, classifying or concentrating ragmentary materials and has for one object to provide, a new and improved process which would be rapid, eicient, easily controlled and can be carried out by means vof apparatuses, of low cost and low complication. l i

In general, it iswell-lmown that if comminuted materials of varying specific gravities are floated in a fluid supporting medium Whose specic gravity approximates the point at which the gravital concentration is to take place, the heavy particles will sink to the bottom and the light particles will oat at the top and so the heavy and the light particles may be separately removed.

When this floating principle is made use of to concentrate materials and when large terial are fed to the classifying tank at a high rate of speed and the concentrated materials are drawn'oii' at a high rate of speed and the result is that heavy particles will be oated off with the light particles and light particles will be entrained down and carried away with the heavy particles and an accurate concentration-especially of the specific gravities not widely different becomes exceedingly diicult. Moreover, because under these circumstances all the concentration must take placein a single horizontal plane, the space in which concentration takes place becomes relatively small and accuracy and capacity both suffer.

propose to increase the volume of the zone within which concentration takes place and to cause gravital concentration not in a single horizontal plane but -in a relatively extended volume of the floating medium. I accomplish this by providing a concentrating tank and maintaining in this concentrating tank a bath of liquid material whose specific gravity increases from the surface downwardly, maintaining such controlled increase of specific gravity at all times during operation. With this arrangement, I prefer to have the specific gravity of the medium at- .the surface slightly less than the specific gravity of the lightest particles so that the capacities are. required, large masses of mat danger of the light particles being entrained with the eflluent at the surface before sufficient time has elapsed for concentration, is reduced to aminimum. The specific gravity of the differential density column increases downwardly until at some point at or near the bottom of the cone the specific gravity is greater than that of the lightest particle. It is evident therefore, that the .llghtest articles cannot sink below this point and) as more material is sent tothe cone, that a bed of the lightest particles is built up from this point, which crowd each other upwardly, so that the excess volume of lightecparticles is discharged at a suitable discharge point. The particles heavier than the medium, of course sink through the medium column and are immediately removed by a suitable discharge device., but the particles of intermediate gravity accumulate below the bed of lighter particles and by virtue of the weight of the supernatant bed of lighter particles are crowded downward to be discharged with the heavier particles.

In order that the light material ma be drawn off from the top of the tank, it 1s of course essential that there be an outflow of the concentrating or separating medium so that there is of necessity a constant flow of this fluid medium from the tank at the top entraining with it the light particles. This overiow passes over ascreen device which separates the lighter particles from the medit um. The medium is returned to the top of the separatory cone near the center by a pump or other circulating device. The specific gravity of the return medium is substantially the same as it was when it overflowed from the cone, but the volume returned is somewhat less, and therefore this difference in volume and density is replaced by liquid fed into the bottom and because of this continuous fiow of liquid to, through and from the tank it is possible by manipulating the density of the inflow and if necessary combining it with diluents in proper proportion to maintain throughout the tank a continued controlled variation in specific gravity as above indicated, the specific gravity being a maximum at the bottom and a minimum at the top. As

the material to be concentrated isfed to the tank it is" gently stirred horizontally, the.

stirring being only sufficient to prevent the floating particles from adhering one to another, to make it easy for the heavier particles to find their way downwardly, each particle sinking to a point at which the specific gravity of the liquid is equal to the specific gravity of the particle. The stirring also insures that conditions will be generally constant throughout each horizontal ,plane intersecting the vertical axis of the tank so as to 'minimize vertical eddy currents which otherwise might tend to interfere with the gradual change in specific gravity of the separating liquid from the top to bottom of the tank. The stirring of the material in the bath associated with the continual feeding in of material to be classified and the continual drawing olf of the heavy material from the bottom and the light material from the top is assisted normally by a concentration of the material caused by the preferred conical shape of the tank so that in general there is a concentration intermediate between the top and bottom of the tank of the materials whose specific gravity is not widely different. This concentration is more or less continuous with the heavier particles being forced downwardly and the light particles being forced upwardly so that there is a continuous outflow of light particles at the top and heavy particles at the bottom.

Illustrating the operation of my device, if I am treating ore, the concentrate, the thing that I want to savefis heavy, the refuse or i tailings are light. the weight of the tailings is more or less constant and I set the apparatus to discharge all the rock or light particles from the top, all the pure ore or heavy particles from Athe bottom. There will be intermediate weight` particles containing some ore which I will want to recover so the device is set so that those intermediate particles will come out at the bottom with the ore. On the other hand, if I am dealing with a product such as coal where the refuse is heavy,` there will very likely' be some coal or bone sufliciently rich in coal that I would want to save it. In that case the apparatus would be set, controlled and operated so that the heavy particles. the stone, would be discharged from the bottom, the light particles, the coal, would be discharged at the top, the intermediate particles, coal with a high percentage of ash, would be discharged from the top or the bottom depending upon the proportion of ash which it was safe to have included with the coal.

The heavier particles are drawn olf from the bottom through any suitable forni of conveyor to a point above the liquid level at which they are discharged, being preferably drawn upwardly along a path outside the concentrating tank, the light particles flowing over the lip of the tank bein discharged and the separating medium W ich is discharged with the heavy and with the light particles may be allowed to drain oif and if necessary to be Washedfrom them and is then fed to any suitable thickening tank where the medium is concentrated or thickcned in its speciic gravity before it is returned to the tank.

Preferably this separating medium comprises water with in suspension the slimes of the material being concentrated. These slimes must be so tine as to approach the colloidal in their action. In most cases it may be necessary to pulverize or grind up this material to obtain these slimes. Under many circumstances, however, there is sufficient of the line material mixed with the coarse so that the material itself furnishes its own slimes but of course the liquid as it is drawn ottl from the material being concentrated is constantly screened or settled or otherwise separated so that its return to the concentrating tank carries only those slimes of sufficiently small size to form a suitable floating medium of controlled specific gravity, although of course under some circumstances a medium of some different character than this might be used and under some circumstances chemicals or chemical so lutions having the desired specific gravity may be used, it being necessary in--any event that the separating medium or liquid maintained in the bath must be susceptible of control so that its specific gravity may be controlled as above indicated. It must be a medium which is substantially permanent and constant in its character and does not readily separate out because if it is'necessary to provide agitation to maintain the slimes distributed throughout the liquid to provide a medium of suitable specific gravity, such agitation will in many instances altogether destroy the concentrating effect by causing undue eddy currents, agitation and violence of flow which would make it impossible for the particles of but slightly different specific gravity to find their way .in an orderly and satisfactory manner down to the level in the tank at which the concentration is to take place.

My invention is illustrated more or less diagraminatically in the accompanying drawing, wherein is shown a diagrammatic sectional view of the apparatus which I propose to use.

Like parts are designated by like characters throughout the specification and drawis *a concentrating cone, larger at the top than it is at the bottom. A1 is a stirrer shaft mounted on brackets, A2 at the bottom and A3 at the top of the cone and driven by any suitable source of power ap lied through of stirrer blades Al5 thereon. It -is understood that this shaft travels at a low rate of speed and the shape of the vanes is such as to produce a very slight and very gentle horizontal stirring movement of the fluid in the cone and the particles suspended in it and tending also to exert an outward pressure on the material in the cone so as to force material floated in the cone especially toward the top outwardly toward the outer periphery thereof.

B is a chute adapted to feed the material to be classified to the cone at the top adjacent the center thereof. B1 is a discharge chute at the top of the cone or tank having a lip or weir B2 over which the light material as it is discharged from the tank flows with a certain amount of the separating fluid. B3 is a screen over which the material travels having a water box B4r beneath it associated with a centrifugal pump B5 which feeds they fluid as it drains ofl the lighter material back to a control and bypass valve B6 and th-ence to the tank through the pipe B7.

C is the discharge throat of the cone or tank. In this case it is shown for convenience as exemplified by a pneumatically controlled flexible iris valve. Leading from this valve is a pipe C1 which discharges to a concentrate boot C2 in which is a scraper wheel C3 adapted to pick up the heavy material, lift it and discharge it through the chute Cl at a point above the common level of -the liquid in the cone or tank A and the boot C. C5 is a pipe controlled by a valve C6 through which the flotation or liquid medium is fed to the boot C2 whereby a current of medium passes down through the boot up through the pipe C1 valve C to the tank so that the flow of the liquid is upward through the concentratingcone. Y'

The means whereby the slimes or fines are mixed with this medium and the means whereby the particles too coarse to be Satisfactory as part of the medium since they form no part of the presentinvention are not here shown and it will be understood that anyy suitable means are shown to insure that the solids in` suspension in the fluid which give i-t its increased specific gravity are of such size and such volume generally in the order ,of colloids that they form an intimate mixture with the liquid itself such as to give the liquid an accurately controlled specific gravity constant throughout and controllable by intcrmixing so that the specific gravity of the liquid or separating mediumA introduced to the tank at the center.

The use and operation of my invention are as follows:

Starting with the concentrating tank containing the bath of separating or concentrat- 1ng medium with the specific gravity of the medium a minimum at the top and a maximum at the bottom and with the stirrer in operation imparting to the bath a rotary motion, material be it coal or anyother mineral or material to be concentrated is All of this material being heavier in specific gravity than .the medium of the bath at the top commences to sink because the specific gravities of the various particles vary among themselves, these particles will sink at vary- .ing rates of speed and they will continue to sink until tlie bath is substantially completely filled with a mass of loosely engaging floating stirred and moving particles, the heavy particles gravitating toward the bott( m, the lighter particles sinking less rapidly and being suspended toward the top. The heaviest particles will pass on to the bottom of the tank, will be Withdrawn by the concentrate conveyor whatever form it may take and be taken away without any substantial admixture of the light particles. The lighter particles as they are left by the heavier particles will tend to concentrate toward the top of the tank and as there is a rapid outflow of medium from the top of the tank and as the centrifugal action of the stirrer tends to propel the particles toward the outer pe-` riphery cf the tank, these lioht particles will be entrained with the lighter specific gravity por-tion of the medium and carried over the lip of the tank.

Because no material to be separated is absolutely homogeneous in so far as its specific gravity is concerned and because separation is done entirely by gravity, a considerable area must be provided so that each particle will have a considerable path along which it may travel while it separates itself by gravity from the other particles, and because the specific gravity of the medium increases downwardly, each particle finds itself at the point at which it will -no longer sink unless it belongs to that group Whose specific gravity is greater than the medium, which group passes out of the tank altogether.. T hus lighter particles which stop in their downward travel a greater or less distance below the surface of the Heating medium will concentrate in the plane at which they cease to go down, will travel outwardly under the linfluence of the stirrer and will be entrained \because if I undertake to provide a oating medium of constant density throughout, all the particles heavier than the floating me- :dium will try to sink to the bottom, all the particles lighter than the medium Will tend or =try to stay at the top and I will make my separation take place entirely in a. single plane. IVhether this can be done or not in the laboratory makes no difference, the point is that in order to get a enflicient capacity to make the device commercially useful, I must provide an arrangement wherein this gravital separation may take place through a considerable range of movement of particles.

lThis is especially true in both ores and coal even though the valuable product in one case is the light material and in the other case the heavy material. Consequently the separation would have to take place at the surface of the cone and if the separation does take place at the surface of the cone, then in order that sufficient fluid may run out from the cone to give capacity much of the mate'- rial would be entrained and carried out before it has had time to be separated.

Owing to the fact that my apparatus is intended for large capacity especially to handle and discharge large amounts of the lighter components being treated, provision must be made for the outflow from the top of the bath or tank of very large volumes of carrier medium. This medium comes ot course from the top of the tank where the density of the medium is a. minimum. As soon as such carrier or separating medium with the lighter sepa.- rated materials have left the tank, the medium is screened out from the materials and immediately returned to the top of the tank, no further treatment of the medium being required other than its return to the tank or bath. A sullicient quantity of the denser portion of the medium is fed in from the bottom and the continuous inflow of this denser medium is controlled to maintain the density ot the medium throughout the tank at the proper point. The sole purpose of the inilow of such dense medium at the bottom isto maintain proper density. As that dense medium travels upwardly it gradually diffuses with the less dense medium from above and this accomplishes and maintains the controlled variable density. Manifestly it would be impossible to feed in to the bottom of the tank sniiicient volume of carrier medium to take care of the discharge of the bull-:y larger proportion of the material treated without setting up upward currents in the tank or bath which would interfere with the proper stratitication of the material in suspension in the medium.

Because the major portion of the medium, perhaps ninety-live percent is returned directly to the tank without further treatment` only some five percent which goes oit adhering to the classilied material and which must he washed ottl the material needs to be treated or thickened before it is returned to the bath, hence-my apparatus and'process do not have to be burdened with a large, expensive and cumbersome thickening apparatus, a thickener being needed only to take care of the remaining five percent which when thickened is returned at the bottom of the tank and furnishes the denser medium.

Because the speci fic gravity of the fluid medium varies from a maximum at the bottom of the column or tub to a minimum at the top and because there is a distinct difference in specific gravity decreasing as you go up the column and because I am dealing with particles having a wide range of specific gravity some greater than the maximum specific gravity of the fluid column, others less than the minimum specific gravity of the fluid column and others in the range between the maximum and minimum of the Huid column, I have three separate conditions to consider.

Those particles which are discharged into the tub and which are heavier than the maximum specific gravity of the fluid will, of course, go tothe bottom of the column and be discharged. rl`hose particles which are discharged into the tub whose specific gravities are less than the minimum will, of course, float to the top of the column and be discharged. T hose particles, and these form the true middlings, whose specific gravities are less than the maximum and greater than the minimum, will be concentrated in the tub between the top and the bottom and will stay there until something happens to get them out. The thing that happens is that as material is fed into the tub, there will be a gradually increased concentration of such particles in the column until those particles which are just about at the separating point, either a little above or a little below the average density of the column will tend to be gradually forced, down if they are heavier than the average,

and up it they are lighter than the average.

so that the crowding action of the material in the tub will gradually force out the middlings if light from the top of the tub, if heavy from the bottom of the tub. This forcing action will not take place until a certain concentration of middlings in the column has taken place. There is a limit to the capacity ofthe column to contain middlings. As that limit is reached. middlings will continue as long as the middling product continues to be supplied to the tub and will continue at substantially the same rate as that at which middlings are fed to the tub, this, however, taking place only after the initial concentration of middlings has occurred,

This action is very different from the action that takes place when material is separated in a tub wherein the specific gravity is the same throughout or wherein there is a sharp line of cleavage between the specific gravities of two float-ing media because in either of those two cases, everything that is too heaify sinks, everything that is too li ht floats o immediately, the separation ta es place and must take place in a sin le horizontal lplane yand there is no possibi ity for the.

Stirrin g when associated with a separating lprocess such as mme 1s desirable onlyyso far as it prevents adhesion of individual particles one to another`in the mass. If the particles did not tend to adhere perhaps owing to surface tension of the liquid, stirrlng could' be dispensed with and would be because it is undesirable in that it tends to slow down or interfere with the accurate concentration of the middlings and the accurate control of the variable density. The more violent the agitation, the more difficult it becomes to maintain an accurately controlled variation in density of the column and the more difficulty I have in controlling this variation in denstiy the more inaccurate becomes the separat-ion.

Itwill be understood that the major mass of material discharged from my concentrator is the light material. be it rock or coal, and that material is discharged from the top of the tub. There is discharged with it a rather large volume of the fluid medium most of which medium is `immediately drained ofi' and returned to the top of the tub. There is a tendency toward a dilution of themedium in the tub as a result of this circulation. This dilution is compensated for by supplying to the bottom of the tub -a relatively small amount of the heaviest or most highly concentrated medium, which medium as it is gradually diluted tends to rise and tends to maintain the controlled gradually upwardly decreased specific gravity of the column.

Because I am dealing with fluid media comprising preferably water mixed with very iine slimes from the material being treated, there is always possibility that difiiculty may arise in controlling the concentration of the heavy medium fed in or controlling the amount and because I am dealing witha co1- umn of fluid medium whose specific gravity varies throughout an appreciable range, the slight local or temporary changes in specific gravity of the medium being fed, in the concentration of the medium being fed, in the volume of the medium being fed, or in the volume of the medium being returned, will not ordinarily materially affect the general situation. The worst that can happen would be to change the median line between the maximum and the minimum concentration somewhere between the top and bottom of the column and will not tend' to materially change the concentrating effect as would be the case if a change in specific gravity took place in a tub where there was a .sharp change in the specific gravity of the medium, and

where the concentration took place in a single concentrating zone. Furthermore, if a sudden change should take place in the spe-4 cific gravity of the medium entering in the bottom and yis detected, an alteration at the i top of the tub can easily be made to compensate for this change in bottom gravity. i

rIhe specific gravity of the liquid separating medium'is controlled, or caused to increase downwardly from the top to the bottom of the tank by supplying continuously to the bottom of the tank, medium of the maximum specific the to Vof the tank, medium of the minimum speci c gravity while simultaneously Vdrawgravity and supplying to ing ofi' from the tank, sufficient of the medium l therein contained to compensate `for theinflow above referred to.

The heavy medium is supplied through the pipe C5 to the concentrate boot C2 whence it flows upwardly through the pipe C to the bottom of the tank, being controlled of course in amount by the valveC". The light s ecific gravity. medium `is fed in prefera 1y through the chute by which the raw material is to be treated. This is preferable because it results in coating the particles of raw material with an envelope of water because normally the diluent or fluid of lightest spe-4 cific gravity is water. -Since the particles are thus coated preliminarily before vthey enter the bath, adhesion of the solid element of the liquid separating medium is thereby? minimized and waste prevented.

Under some circumstances it is sutliicient to merely wet down the raw materials as they go in or before they are discharged to the chute. Under other circumstances a separate hose pipe may be provided which discharges into the chute or, if desired of course, could be discharged directly into the tank. Under other circumstances the diluent is provided by washing the gangue as it travels over the screen B3, under which circumstances the separating medium passin over the lip B2 with the angue, is diluted efore it returns to the tan through the pipe B".

It must be very definitely understood that this control of specific gravity of the liquid is not in any sense or under any circumstances a result of the settlement downward of parazi` ticles in suspension, nor is it in any sense a Y result of agitation of the liquid because the preferable flotation or separating liquid medium comprises water and ne particles, so fine as to approach in their nature colloidal action and under these circumstances these i with solids which require any agitation to preserve the tluidic roperties, when in suspension of a liquid, cause since I propose to make a separation of particles having a very narrow range of speciticravity variation, any such agitation woul vent separation. What I pro ose to use on the other hand, are mixtures o finely divided solids with water, which materials when l0 finely divided, form suspensions in water that approach solutions in their physical propertles. c

Thus the control of the specific gravity of the liquid in the tank results from feeding to the bottom of the tank, liquid of highest -specific gravity and feeding to the top of the tank, liquid of lowest specific gravity, so-that the upward diiusion of the heavy liquid and the downward diffusion ofthe 90 light liquid, when the relative amounts are properly controlled, result in maintaining constantl during operation, throughout the tank, a isiiid separating column whose specific gravity is a minimum at the top, a maxi- 35 mum at the bottom and decreases gradually from the top to the bottom without any zoning orjsudden change in specific gravity.

The separating medium which I use in carin out my process may best be characterized as a self-maintaining medium. By

this term I mean a medium, perhaps a solution, `perhaps a liquid having solids in susnsion, which, so long as it is in the separat- 111g zone, will retain its normal fiuidic condition without any agitation or extrinsic help whatsoever, and which, when controlled quantities of the medium of high specific gravity are added to the bottom and of low specific gravity are added to the top of a 0 liquid column, will during operation, maintain a gradual continuous controlled even variation in specific gravity from top to bottom of the column. f

By the term continuous gradual change in specific gravity of the medium, I mean to indicate a situationy wherein the curve of specific gravity variation from top to bottom of the bath, is a continuous line as distinguished from a broken line. In other Words the gradual continuous change in specific gravity is a change which takes place regularly from top to bottom of the bath as distinguished from a bath containing a plurality of superposed zones of different specific gravities.

The upward current which occurs in connection with carrying out my process, must of necessity be a very feeble upward current, 50 and by feeble I mean an upward current of such low velocity that it exerts no measurable lifting effect whatsoever on any of the particles floating in the bath, sothat their separation takes place as a result of differences in specific gravity only, and under no circumentirely pre` stances and to no'extent as a result of being supported by a fluid current.

The stirring of the bath must be v ery gentle because it is solely for the purpose of maintaining horizontal uniformity of the medium and because if the stirring is more violent than just suicient for this purpose, it will result in setting up eddy currents and causing vertical movement o`f the bath, which will materially interfere with the specific gravity separation, and with the essential continuous gradual chan e in the specific gravity of the fluid column om top to bottom.

I claim:

l. A ravity separating process which consists 1n feeding material to be separated into and suspending it in a substantially selfmaintaihing fluid bath, controlling the specific gravity of the bath so that it increases continuously and graduall from the top downwardly, separating t e material between the top and bottom of the bath, gently stirring the bath and withdrawing the llghter particles from the upper and the heavy particles from the lower portion of the bath.

2. A gravity separating process which consists in feeding materialvto be separated into and suspending it ina'substantially selfmaintaining fluid bath, controlling the specific gravity of the bath so that it increases continuously and gradually from the top downwardly while maintaining a continuous feeble upward current in the bath, separatin the material between the top and bottom o the bath, gently stirring the bath and withdrawing the lighter particles from the upper and the heavy particles from the lower portion of the bath.

3. A gravity separating process which consists in feeding material to be separated into and suspending it in a substantially selfmaintaining iuid bath, controlling the specific gravity of the bath so that at the surface it is lighter than the specific gravity of the light particles and so that it increases continuously and gradually toward the bottom until a point is reached at which the specitic gravity is somewhat heavier than the specific gravity at which separationof the material is to be made, concentrating the material at a p'oint between the top and bottom of the bath, gently stirring the bath and withdrawing the lighter particles from the upper and the heavy particles from the lower portion of the bath. f

4. A gravity separating process which consists in feeding material to be separated into and suspending it in a substantially self-maintaining fluid bath, controlling the Aspecific gravity of the bath so that at the surface it is lighter than the specific gravity of the light particles and so that it increases continuously and gradually toward the bottom until a point is reached at which the specific gravity is somewhat heavier than the specific gravity atwhich separation of the material is to be made, while maintaining a continuous4 gently upward current in the bath, concentrating the material at a point between the top and bottom of the bath, gently stirring the bath and withdrawing the lighter particles from the upper and the heavy particles from the lower portion of the bath, the stirring being substantially sufcient only to maintain horizontal uniformity in the bath without appreciable vertical movement of the fluid and solids resulting from such stirring.

5. A gravity separating process which consists in feeding material to be separated into and suspending it in a substantially selfmaintaining fluid bath, controlling the specific gravity of the bath so that it increases continuously and gradually downwardly, concentrating the material intermediate ythe top and bottom of the bath and withdrawing the lighter particles from the upper and the heavy particles from the lower portion of the bath.

6. A gravity separating process which consists in feeding material to be separated into and suspending it in a substantially selfmaintaining fluid bath, controlling the specific gravity of the bath so that at its upper level it is slightly lower than the specific gravity of the light particles and so that it increases continuously and gradually downwardly until a specific gravity is reached which is somewhat loss than the specific gravity of the heavy particles, concentrating the material at a point between the top and bottom of the bath and withdrawing the lighter particles from the upper and the heavy particles from the lower portion of the bath.

7 A gravity separating process which consists in feeding material to be separated into and suspending it in a substantially selfmaintaining fluid bath, controlling the specific gravity of the bath so that it increases gradually from the top downwardly, gently stirring the bath and withdrawing the lighter particles from the upper portion and the heavy particles from the lower portion thereof, the stirring being substantially suflicient only to maintain horizontal uniformity in the bath without appreciable vertical movement of the fluid and solids resulting from such stirring.

8. A gravity separating process which consists in feeding material to be separated into and suspending it in a substantially selfmaintaining fluid bath, controlling the specific gravity of the bath so that at its upper level it is slightly lower than the specific gravity of the light particles and so that it increases gradually downwardly until-a specific gravity is reached which is somewhat less than the specific gravity of the heavy particles concentrating the material at a point between the top and bottom of the bath,

gently stirring the bath, and withdrawing the lighter particles from the upper and the heavy particles from the lower portion of the bath, the stirring being substantially sufficient only to maintain horizontal uniformity in the bath without appreciable vertical movement of the fluid and solids resulting from such stirring.

9. A gravity separating process which consists in feeding material to be separated into and suspending it in a substantially selfmaintaining fluid bath, controlling the specific gravity of the bath, so that it increases continuously and gradually from the top downwardly and withdrawing the lighter particles from the upper portion and the heavy particles from the lower portion thereof.

10. A gravity separating process which consists in feeding material to be separated into and suspending it in a substantially selfmaintaining fluid bath, controlling the specific gravity of the bath so that at its upper level it is slightly lower than the specific gravity of the light particles and so that it increases continuously and gradually downwardly until a specific gravity is reached which is somewhat less than the specific gravity of the heavy particles, and withdrawing the lighter particles from the upper and the heavy particles from the lower portion of the bath.

11. The process of classifying material of different specific gravities which consists in forming a separat-ing zone containing a substantially self-maintaining liquid medium, the density of which continuously and gradually decreases from the bottom to the top thereof, supplying a continuous stream of the comminuted particles to be classified to the separating zone, gently stirring the fluid and the material floating in it and forming intermediate the top and bottom of the separating zone, a relatively compacted middling zone of floated material,continuingthe supply Ofcomminuted particles thereto and vcausing the heavy materials to be forced downwardly, the light materials to be forced upwardly from the middling zone and withdrawing the light materials from the top and the heavy materials from the bottom of the flotation zone.

12. The process of classifying materials of different specific gravity which consists in feeding a continuous stream of solid particles into a separating zone containing a separating medium, the density of which varies continuously and gradually lfrom top to bottom of the zone so that the density at the bottom is approximately the density at which separation is to take place and the density at the top is less than the density of the heavier particles, gently stirring the particles floating in the medium forming a middling zone intermediate the top and bottom level of the flotation material, the cross sectional area of which measured in a horizontal direction is less than the cross sectional area of the zone at the top and greater than the cross sectional area of the zone at the bottom, continuing the supply 5 of material to said zone whereby the heavy particles are forced down from the bottom of the middling zone, the lighter particles are forced upwardly from the top of the middling zone and then withdrawing the heavy parti- 10 cles from the bottom and the light particles from the top of the separating zone the stirring being substantially suflicient only to maintain horizontal uniformity in the bath without appreciable vertical movement of the fluid and solids resulting from such stirring.

13. The process of gravitally classifying materials which consists in continuously feeding a stream of fragmentary material made up of particles of different specific gravities into a substantially self-maintained Huid concentrating bath, controlling the specific gravity of the bath so that its specific gravity toward the top is greater than the specific gravity of the heavy particles and so that its specific gravity increases continuously and gradually downwardly toward the bottom, agitating the bath with its suspended burden of material being concentrated, concentrating the middlings at a point intermediate the top and bottom of the bath and withdrawing from the bath at the top the lighter particles, and withdrawing from the bath at the bottom the heavier particles.

14. The process of gravitally classifying materials which consists in maintaining a bath of substantialy self-maintaining liquid floating medium whose specific gravity decreases from the bottom upward, supplying material to be classified to the bath, discharging from the top of the bath a relatively large volume of the medium with the classified material, separating the medium from the classified material after they have left the bath and immediately returning such medium to the top of the bath, withdrawing the heavier particles from the bottom of the bath and continuously supplying to the bottom of the bath a relatively small proportion of medium to maintain a controlled gradual upward decrease in specific gravity of the medium, washing that part of the medium remaining associated with the classified material off such material, thickening it and returning it as part of the denser medium at the bottom of 'the bath.

15. The process of separating materials of different specific gravities which consists in forming and maintaining a substantially selfmaintaining fluid separation column wherein the specific gravity increases gradually from the top downwardly, discharging into the column raw material to be separated, and wthdrawing from the column, at the bottom,

material particles of relatively high, and at the top material particles of relatively low specific gravity.

16. The process of separating materials of different specific gravities which consists in providing a substantially self-maintaining fluid separating column, continuously supplying to the bottom of the column fluid having relatively high specific gravity, continuously supplying to the top of the column fluid having relatively low specific gravity and withdrawing from the column sufficient fluid to compensate for the amount thus supplied, discharging into the column raw material to be separated and withdrawing from the column at the bottom material particles of relatively high, and at the top material particles of relatively low specific gravity.

17. The process of separating materials of different specific gravities which consists in providing a fluid separating column, continuously supplying to the bottom of the column fluid having relatively high specific gravi'y, continuously supply`ng to the top of the column fluid having relatively low specific gravity, and withdrawing from the column sufficient fluid to compensate for the amount thus supplied, discharging into the column raw material to be separated and withdrawing from the column at the bottom material particlesof relatively high, and at the top material particles of relatively low specific gravitv, and controlling the relative quanities of the fluid supplied to top and bottom of the column to cause the specific gravity of the separatng column to increase gradually and continuously from' thc top "ownwardly.

18. The process of separating materials of different specific gravities which consists in providing a fluid separating column, continuously supplying to the bottom of the column flu'd having relatively high specific gravity, continuously supplying to the top of the column fluid having relatively low specific gravty and withdrawing from the column sufficient fluid to compensate for the amount thus supplied, discharging into the column raw material to be separated and withdrawing from the column at the bottom, material particles of rela'ively high, and at the top material particles of relatively low specific gravity, and controlling the specific gravities of the fluid supplied to the top and bottom of the column to cause the specific gravity of the separating column to increase downwardly.

19. The process of separating materials of different specific gravities which consists in providing a fluid separating column, continuousl supplying to the bottom of the column fluit? having re atively high specific gravity, continuously supplying to the top of the column fluid having relatively low specific gravity and withdrawing from the column sufficient fluid to compensate for the amount thus supplied, discharging into the column Lacuna raw material to be separated and withdrawing from the column at the bottom, material particles of relativel high, and at'th top material particles o relatively low specilc gravity, and controllin `the quantity and specific gravity of the uid suppliedto the top and bottom of the column to cause the specific gravity of the'separating column to increase from the top downwardly.

Signed at Prescott, count of avapai and State of Arizona, this 18th ay of Jul 1932.

CHARLES ERB WUEN CH. 

